Pexpect and SSH

If you try to use the previous telnet example and just plug into a ssh session, you might find yourself pretty frustrated. You always have to include the username in the session, ssh new key question, and more such. There are many ways to make ssh sessions work, but luckily, Pexpect has a subclass called pxssh, which specializes setting up SSH connections. The class adds methods for login, logout, and various tricky things to handle many situation in the ssh login process. The procedures are mostly the same with the exception of login() and logout():

>>> from pexpect import pxssh
>>> child = pxssh.pxssh()
>>> child.login('172.16.1.20', 'cisco', 'cisco', auto_prompt_reset=False)
True
>>> child.sendline('show version | i V')
19
>>> child.expect('iosv-1#')
0
>>> child.before
b'show version | i VrnCisco IOS Software, IOSv Software (VIOS-ADVENTERPRISEK9-M), Version 15.6(2)T, RELEASE SOFTWARE (fc2)rnProcessor board ID 9MM4BI7B0DSWK40KV1IIRrn'
>>> child.logout()
>>>

Notice the 'auto_prompt_reset=False' argument in the login() method. By default, pxssh uses the shell prompt to synchronize the output. But since it uses the PS1 option for most of bash or Csh, they will error out on Cisco or other network devices.